The present invention relates generally to a data processing local area network, for example an Ethernet network. To be more precise, the invention relates to a method of providing a remote power feed to a terminal in a data processing local area network and also to a remote power feed unit, a concentrator, a repeater (also known as a hub), and a terminal adapted to implement the method.
FIG. 1 is a diagram showing, by way of illustrative and non-limiting example only, an Ethernet data processing local area network which includes a local area network server 1, a switch 2, a repeater 3 and N terminals 41 to 4N which include telephones operating in Voice over IP (VoIP) mode. The server 1 is connected to the Internet 0 and receives packets complying with the Internet protocol (TCP/IP). The packets of a given call are routed via the switch 2 and the repeater 3 to a terminal such as the telephone 41 which is connected to the repeater by a 8-wire line L terminated with RJ45 connectors.
The terminals connected to a data processing local area network (for example personal computers, printers, etc.) are conventionally connected locally to the mains electrical power supply. 110 V or 220 V power cords independent of the data connections are therefore used to supply power to the terminals. This solution makes installation of the local area network more difficult:
Using two cables causes problems of congestion which can additionally impede the free movement of persons.
It creates electrical hazards.
In the case of a telephone, a local connection to the mains electrical power supply has the additional drawback that the telephone is out of service in the event of a mains power outage, in particular in the event of a fire or natural disaster. This is why conventional telephones receive a remote power feed from their local exchange, which includes emergency batteries.
It is therefore desirable for some of the terminals connected to a data processing local area network to be provided with a remote power feed via the same connection as is used to send and receive data. It is also desirable to be able to install the remote power feed unit anywhere on the line L (either inside or outside a repeater 3), to enable easy addition to an existing network.
One way of transmitting a remote power feed current is to use two of the eight wires of the line L: four other wires form two pairs of wires respectively used to transmit and to receive data. Another method, referred to as a phantom circuit, connects the two terminals of a power supply generator in the remote power feed unit to respective center-taps of a winding of a transformer connected to the pair for receiving data and a winding of another transformer connected to the pair for sending data. At the terminal, the supply voltage is obtained between respective center-taps of a winding of a transformer connected to the pair for receiving data and a winding of another transformer connected to the pair for sending data.
In both cases, providing a remote power feed to the terminal via the data processing local area network has the disadvantage that the remote power feed unit supplies power to a terminal xe2x80x9cblindxe2x80x9d. The RJ45 connector at the end of the line L could be plugged into a terminal other than a telephone (for example a personal computer, a printer, etc.). There is a risk of damaging the electrical circuits of that terminal. The RJ45 connector of a terminal is generally used in the following manner:
Four of the eight wires are separated into two pairs for respectively sending and receiving data. The terminal includes a transformer having one winding connected to the receive pair and a transformer having one winding connected to the send pair, each of these windings having a center-tap which can be connected to a reference potential via a low-resistance resistor.
Four other wires are not used and are grounded, often via a combination of resistors and capacitors, to eliminate any crosstalk induced by the data signals in the first four wires and to reduce unwanted electromagnetic emission. If a relatively high remote power feed voltage, for example 48 volts, is applied to that combination of resistors and capacitors, or to the resistors connected to the center-taps of the transformers, the resistors can be destroyed by the current flowing in them.
The invention therefore aims to solve this problem by proposing a method of providing a remote power feed to a terminal in a data processing local area network and systems for implementing the method which prevent all risk of damage if a terminal is plugged in which is not one of the terminals adapted to receive a remote power feed via the network.
The invention firstly provides a method of providing a remote power feed to a terminal in a local area network, the method entailing:
producing at least one detection signal on at least two conductors of a line for connecting the local area network to a remote terminal, that signal having an energy such that the terminal cannot be damaged under any circumstances,
detecting the presence of a remote terminal adapted to receive a remote power feed by detecting the presence of predetermined impedance in the remote terminal on the basis of a current created by the test signal in that line, and
sending a power supply current in that line when the presence of a terminal adapted to receive a remote power feed is detected.
The above method prevents all risk to the terminals because the remote power feed current is sent only if the terminal has been identified as one which is adapted to receive a remote power feed. The intensity and duration of the detection signal are chosen so that the operation of detecting the terminal cannot cause any damage if the terminal is not one which is adapted to receive a remote power feed.
In one particular embodiment of the invention, to detect a predetermined impedance in the remote terminal, the presence of a capacitor in the remote terminal is detected.
The resulting method is particularly simple to implement. The capacitance of the capacitor is chosen so that it is significantly different from that of the line. Measuring a capacitive impedance then indicates a terminal adapted to receive a remote power feed. The capacitor can shunt two conductors used for the remote power feed without affecting transmission of the remote power feed current, which is a direct current.
In another particular embodiment of the invention, to detect a predetermined impedance in the remote terminal, the presence of a short-circuit in the remote terminal is detected.
The resulting method is particularly simple to implement, and therefore advantageous, when the short-circuit can be applied between two conductors of the line which are chosen so that the short-circuit does not impede either the remote power feed or sending and receiving data.
In a preferred embodiment of the invention, to detect the presence of a capacitor in the remote terminal:
an alternating current test signal is applied to the line and it is verified that the remote terminal does not behave like an open circuit for that signal,
a direct current test signal is applied to the line and it is verified that the remote terminal behaves like an open circuit for that signal, and
the method concludes that a terminal adapted to receive a remote power feed is present if the results of both tests are positive.
In one particular implementation of the invention a remote power feed method is suited to a line including two pairs for sending/receiving data and each enabling the transmission of a remote power feed current in common mode and other conductors which can also be used for a remote power feed. In the method, detecting a remote terminal adapted to receive a remote power feed entails:
performing a first test to detect if the terminal is adapted to receive a remote power feed via the two pairs for sending/receiving data,
performing a second test to detect if the terminal is adapted to receive a remote power feed via the other conductors that can also be used for a remote power feed,
sending a remote power feed current in the two pairs for sending/receiving data only if the first test shows that the terminal is adapted to receive a remote power feed via those two pairs, and
sending a remote power feed current in the other conductors that can also be used for a remote power feed only if the second test shows that the terminal is adapted to receive a remote power feed via those other conductors.
In one particular embodiment of the invention the first test consists of detecting the presence of a first predetermined impedance in the terminal on the basis of a current created by a first test signal in the two pairs for sending/receiving data and the second test consists of detecting the presence of a second predetermined impedance in the terminal on the basis of a current created by a second test signal in the other conductors.
One of the two predetermined impedances is preferably a short-circuit and the other predetermined impedances is preferably a capacitance.
The resulting method enables the remote power feed current to be increased, because it enables up to eight conductors of an Ethernet line to be used and can discriminate between several types of terminal adapted to receive a remote power feed that have different power consumptions. For example:
If it detects that the terminal is not one which is adapted to receive a remote power feed via the available conductors in an Ethernet line, but is adapted to receive a remote power feed via a phantom circuit using the pairs for sending and receiving data, this means that the terminal has a low power consumption, in which case it is possible and sufficient to send a remote power feed current via the phantom circuit.
If it detects that the terminal is adapted to receive a remote power feed via the available conductors in an Ethernet line and is also adapted to receive a remote power feed via a phantom circuit using the pairs for sending and receiving data, this means that the terminal has a high power consumption, in which case it is possible and necessary to send a remote power feed current via the phantom circuit and a remote power feed current via the available conductors.
The invention secondly proposes a terminal adapted to implement the above remote power feed method, the terminal including at least one predetermined impedance connected to at least two conductors of the line and which identifies the terminals adapted to receive a remote power feed.
The predetermined impedance preferably includes a very much higher capacitance than that of terminations routinely connected to the ends of the line in terminals that are not adapted to receive a remote power feed but are adapted to be connected to the local area network concerned.
The invention thirdly proposes a remote power feed unit for implementing the method and which includes:
means for producing at least one detection signal on at least two conductors of a line for connecting the local area network to a remote terminal, that signal having an energy such that the terminal cannot be damaged under any circumstance,
means for detecting the presence of a remote terminal adapted to receive a remote power feed by detecting the presence of a predetermined impedance in the remote terminal on the basis of a current created by the test signal in that connection, and
means for sending a power supply current in the line when the presence of a terminal adapted to receive a remote power feed is detected.
One particular advantage of the above remote power feed unit is that it can be installed anywhere on the line (inside or outside a repeater), because it can operate entirely independently of the units of a repeater.
Another object of the present invention is to propose a repeater and a concentrator which can be inserted (separately or together) between a remote power feed unit and a terminal (or another equipment unit adapted to receive a remote power feed, such as a repeater or a concentrator) without interfering with discrimination or the remote power feed.
The present invention fourthly proposes a repeater adapted to receive a remote power feed and adapted to be included between a network equipment unit including a remote power feed unit and another network equipment unit in a local area network,
the repeater including a power supply unit powered by a remote power feed and whose input is connected in parallel with the power supply input of the other network equipment unit to the conductors of the line that provide the remote power feed, and
the power supply unit having an input impedance whose modulus is very much higher than the modulus of the input impedance of the power supply unit which is characteristic of equipment units adapted to receive a remote power feed likely to be connected downstream of that repeater.
The resulting repeater does not interfere with discriminating between an equipment unit that is adapted to receive a remote power feed and an equipment unit that is not adapted to receive a remote power feed, because the power supply input impedance detected by an upstream remote power feed unit remains approximately the same when the power supply input impedance of the repeater is connected in parallel with that of another network equipment unit. Also, the other network equipment unit and the repeater both receive a remote power feed from the upstream remote power feed unit, because their respective power supply inputs are connected in parallel to the conductors of the line that provide the remote power feed.
The present patent application fifthly proposes a concentrator adapted to be inserted into a line between a network equipment unit including a remote power feed unit and at least one other network equipment unit in a local area network,
the concentrator including, for each of its ports adapted to be connected to another network equipment unit, a remote power feed unit which includes:
means for producing at least one detection signal on at least two conductors of a line for connecting the concentrator to another network equipment unit, that signal having an energy such that the other network equipment unit cannot be damaged under any circumstances,
means for detecting the presence of another equipment unit adapted to receive a remote power feed by detecting the presence of a predetermined impedance in that other equipment unit on the basis of a current created by the test signal in the line, and
means for sending a power supply current in the line when the presence of another equipment unit adapted to receive a remote power feed is detected.
The resulting concentrator provides a remote power feed to downstream equipment units that are adapted to receive a remote power feed and does not provide a remote power feed to equipment units that are not adapted to receive a remote power feed because it includes an additional remote power feed unit specific to each of its ports, that additional remote power feed unit operating in a similar manner to but independently of the upstream remote power feed unit in a network equipment unit such as an Ethernet switch or another concentrator.
In a preferred embodiment of the invention, the concentrator is itself adapted to receive a remote power feed and includes at least one predetermined impedance connected to at least two conductors of the line connected to the upstream network equipment unit and which is characteristic of the power supply input of equipment units that are adapted to receive a remote power feed.
The resulting concentrator can be inserted into a line without compromising the advantages for that line of the remote power feed, because it can itself be detected as adapted to receive a remote power feed and therefore receive a remote power feed.